THMotorsports

At 700lb front, the car is still able to compress the spring enough that you get a fair amount of droop. ~1.36" in the front. If your springs are loose, you get a little bit more, though it relies only on the gas pressure of the shock to maintain contact once the spring is unloaded. In any event, this is probably why Brian said they're not necessary. With higher rates (14k+ front, 12k+ rear) the assist springs are more necessary. Zero rate springs only help to keep the spring seated. Assist springs have rate to them, this helps overcome the rebound force of the shock. I usually use 3kg assist springs, it's soft enough that the spring is fully compressed, which means that you're only relying on the main rate to control roll. But it has enough rate that it's able to improve droop, and maintain contact/grip.

AlpineFD

Sprung Weight is what compresses the spring, not the corner weight, you have to subtract the unsprung weight.

There is a motion ratio (leverage ratio) for both the spring and the sway bar (they are different), so you can't just multiply the weight like that.

for calculating weight transfer, i only use a simplified version of the formula to check for shock travel at max G.
but to get a very accurate weight transfer # in different dynamic situation, you have to take the COG and track width into account, plus the sway bar/spring rate for lateral load distribution, probably even more variables, that will be something for a real suspension engineer to calculate.

Nate Tempest

Ah, right, good point that it's only the sprung weight compressing the spring.

What's the simplified formula you use to estimate shock travel? I did take into account the COG and the track width to determine the total weight transfer, so that should be fairly accurate. You're saying that the split front to back is not just linearly related to front to back spring + sway bar spring rates though? I agree that there will be lateral loading on the springs as well, and that I'm not taking that into account, but I would think you'd get a decent approximation just looking at the vertical forces on each side, and for that you should be able to just add the spring and sway bar spring rates, right?

BuggyofMildDiscomfort

You will get overshoot from the chassis movement - it doesn't accelerate and decelerate instantly, and you don't have critical damping to stop the overshoot (well, not unless you've screwed up on your damper settings for a road/track car anyway, aero and rally cars are different)

thomsbrain

Holy understeer, Batman!

Chibo

Number of ways to get it to rotate

Nate Tempest

Actually it's very difficult to get it to understeer. Tends toward oversteer in most situations. Keep in mind this is with square tires and more camber in front than rear. Still, I was pretty surprised too when I looked up the front sway bar rate—I'd expect it to be understeering too, just looking at the numbers. FWIW this setup is basically copied from Brian Karwan (Karcepts) with only minor tweaks, and he used very competitively at Nationals. It's similar to what a lot of people use in STR. Bit of a tangent, but I'd definitely be interested if someone can explain why it _doesn't_ understeer, given how much more weight transfer is happening at the front than the rear.

Here's an example of oversteer on turn-in (although to be fair my rear tires were overheated here, but part of the reason the rears are hotter than the fronts after a few hot laps is because it is biased toward oversteer). Edit: seems like the embedded version doesn't jump to the right time. Go to 5:55. (Oh, and just in case someone asks, it wasn't the gear shift; rev matched and the shift was done before turning in when the rear end got loose.)
If you go back to about 4:00 and watch the last lap you'll see a few more little ones. (Sorry about the sound; forgot to put the cover on the gopro mic for this one.)

Nate Tempest

Fair enough. But say you do dynamically unload the front enough for the tender spring to start extended—would you actually want that? When hitting a dip softer springs are nice because they allow the wheel to follow the contour better. But in pitch or roll (sustained or dynamic), softer springs would mean more body roll, which probably wouldn't be what you want. In order to be useful, you'd need to be in the middle of a significant dynamic event that's thrown the weight off the front wheels temporarily, AND to hit a dip at the same time, no?

BuggyofMildDiscomfort

A bit of extra body roll is far better than a sudden spike in tyre loadings.

thomsbrain

Of course I'm not in the car, but to me that looks like what happens when a car that generally understeers is loaded up enough through forward weight transfer to finally have the front wheels bite, suddenly kicking the tail out. Nice save, by the way! Fast hands. STR cars are generally set up extremely understeery because they need quick steering response more than maximum steady-state traction like a road-course car.

My car has square tires, more front camber than rear, no rear toe, half the front sway bar rate of yours, stiffer rear springs than front, and roughly a 60% front roll bias compared to your 72%, but it still tends towards understeer in steady-state cornering, and I can go full throttle on corner exit in second gear. If anything, I want more rotation and intend to shift my bias rearward another few percent.